A final aspect of time to be addressed is the duration between instants. In doing so, one must distinguish between two separate issues. On one hand there is a natural notion of time that can be inherited from space-time itself; this being the local proper time \(\delta \xi _{x}^{\perp }\)  experienced by an observer at the point \(x\)  (see e.g., [1]}). On the other hand, however, notions of time and duration cannot themselves be divorced from those of dynamics and change. Indeed, the two are closely bound together.
